I'm not really sure about your exact requirement, but should it's really that simple regex, simple concatenation will do as well.

my @orig = qw(a,b c,d e,f);
my $extra = 'hi';
my @new = map { $_ .= ",$extra" } @orig;
print "orig: [@orig] => new: [@new]\n";
# orig: [a,b,hi c,d,hi e,f,hi] => new: [a,b,hi c,d,hi e,f,hi]
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This way, you append the line and return it as well from map().